Method of making greases



United States Patent N0 Drawing. Filed Sept. 28, 1060, Ser. No. 58,880 6 Claims. (Cl. 252-41) This invention relates to the manufacture of lubricating greases. More particularly, this invention relates to an improved process for the manufacture of greases thickened with lithium soaps of hydroxy fatty acids.

A conventional high temperature method employed in the manufacture of greases which are difiicult to prepare in satisfactory smooth form such as greases thickened with lithium soaps of hydroxy fatty acids, includes shock cooling a hot grease mixture either statically or with agitation so that the melted soap crystallizes in the form of very fine particles. Recently, methods have been discovered which include cooling the grease mixture at a relatively low rate while employing various techniques for the avoidance or reduction of super cooling. However, these methods have been partially ineffective as a long-fibered grease is formed which has a strong tendency to agglomerate during the stirring or the agitation stages which are employed in these commercial methods. Furthermore, the agglomerates which are formed are not easily separated by milling the grease according to conventional procedures. This difficulty therefore results in a deterioration of product quality and poor yields.

In the processing of lithium-lZ-hydroxy stearate greases, normally dehydration temperatures in excess of 400 F. are employed in order to obtain maximum gelling effect of the soap thickener. When forming by known methods a lithium-lZ-hydroxy stearate grease using a maximum temperature of about 350 F., the resulting grease is a satisfactory product but yields, i.e., hardness for a given soap content, are less than obtained in the high temperature procedure. Due to the relatively high cost of the soap thickener, a grease having the highest yield or lowest soap content for a given consistency is highly desirable.

Thus the need for a process which gives a high-yieldloW-soap content lithium grease which can be prepared in the conventional grease-making equipment capable of effecting a maximum temperature of about 300350 F. is clearly evident. The process of this invention overcomes these above-mentioned problems and facilitates the manufacture of a high-quality lithium-lZ-hydroxy stearate grease using conventional steam kettle temperatures, i.e., a maximum of about 300 to 350 F. during dehydration.

The improved method of this invention includes heat ing in grease-forming proportions a mixture of an ester of 12-hydroxy stearic acid, a suitable mineral or petroleum lubricating oil and an aqueous solution of a soluble lithium neutralizing compound to form a grease composition using a maximum temperature of about 300 to 350 F. The lithium soap is formed in situ in all or a portion, for instance, at least about an equal part based on the soapforming ester, of the mineral base oil and a more or less homogeneous liquid mixture of the soap, water and lubricating oil is treated until it is essentially dehydrated. The mixture is then cooled and a grease composition is obtained. The process of the present invention involves recycling the mixture at least during the initial dehydration phase, that is, While the temperature is in the range from approximately 200 to 350 F., through a shearing device so that grease formed is turned over rapidly and subjected to shear. In accordance with the present invention, the recycling is conducted during the major portion or even essentially all of the period wherein the temperature is in the range of about 200 to 260 F. but can continue through the major portion or essentially all of the approximate 200 to 350 F. range. The initial dehydration period may include the soap-forming reaction.

Recycling to the shearing means only after the dehydration period, however, has been found to be ineffective in the low temperature (350 F. maximum) processes. Thus the recycling of the present invention should be from essentially the start of soap fiber formation (i.e., water removal causing soap crystallization). The period of dehydration ranging from about 200 to 260 F. is generally the time it takes for the Water content of the grease constituents to drop from about 5 to 15% e.g. about 10% to a content of about 2 to 0.3% or less. This period can be easily determined by measuring the water content of the recycle material. The rate of recycle should be that necessary to recycle the entire batch of grease constituents rapidly during the dehydration period. The rate of recycle is dependent on the rate of dehydration, temperature etc. but is generally a rate that gives at least about 0.02 batch turnover per minute, preferably at least about 0.1 batch turnover per minute. Some improvement in yield is obtained when the batch turnover is less than .02 per minute. The rate can be as great as desired but little if any reason has been found for exceeding a rate of about 1 batch turnover per minute.

The saponifiable materials employed in the production of the soaps of the present invention are the esters of 12- hydroxy stearic acid, preferably the lower alkyl, e.g., of up to about 8 carbon atoms, esters of IZ-hydroxy stearic acid, such as the methyl ester or the glyceride. The saponifying agent used for the in situ formation of the soap may be any Water-soluble lithium neutralizing compound as, for example, the inorganic oxides, hydroxides and carbonates of lithium. The neutralizing component provides essentially complete neutralization or conversion of the ester to the soap although some free ester or lithium base may remain. In the final grease the lithium 12- hydroxy stearate is provided in an amount sufiicient to exert in the base oil the essential thickening action, and the soap will usually be about 5 to 15% of the grease composition and the major part of the total base-oil thickening component.

The oleaginous liquids employed in the greases produced by the method of this invention may be any suitable oils of lubricating characteristics, including the conventional mineral lubricating oils. Suitable mineral oils include those having viscosities in the range from about to 2,000 seconds Saybolt Universal at 100 F., and may be either mixed, naphthenic or parafiinic in type, or blends thereof.

The greases may also contain various additives of the usual types such as corrosion inhibitors, oxidation inhibitors, antiwear agents, extreme pressure agents and so forth. Preferably, they contain an oxidation inhibitor, which may suitably be an oxidation inhibitor of the amine type, such as diphenylarnine, phenyl alpha naphthylamine or tetramethyldiaminodiphenylmethane. Compounds of this type may be added either before or during the cooling down process. They are preferably added while the temperature of the grease is between about 300 F. and about 180 F.

In the process of this invention the mixture of the fatty constituents and the oil is usually raised to a temperature of about 190-220 F. to melt the fatty material before the addition of the lithium base. The steam is then turned on the kettle and the recycle is started to obtain method of preparing the greases of the present invena pressure of about 40 p.s.i. g., or more in the recycle tion. line. Dehydration is then effected by raising the tem- EXAMPLE I perat'um ito absut 300 350 preferably to '24 lbs of lithium hydroxide monohydrate were disabout 320450 D unng the pal-10d of dehydration solved in 12 lbs. of water and then added at a temperathe batch of constituents are recycled under pressure 10 mm of about F to a mixture of melted fats and around the kettle and through a restricted orifice-contain- 120 lbs of mineral lub'ricatinu Oil The melted fats ai fi fi 1 b prised 1.5 lbs. of beef tallow and 13.5 lbs. of hydroe means eyed ls.prefera of l type genated castor oil. The mineral oil had a gravity API 1 igwes very efiecnve sheanng and impel-8mg of 23.2 viscosity S'US at 210 F of 80.7 and a viscosity non with only a small amount of kneading action 15 ind x (if 62 5 The constituents were then heated and globe valve, colloidal mill etc. A particularly suitable rec;c1ing begun through a globe valve with a demce fol.- thls i f 1S a .Shear Valve through Whlch the presure drop across the valve of 50 pounds per square grease mixture 1S passed with a substantial pressure drop inch and a recycle rate of 22 4 pounds per minute when into a Confined p.assag.eway so that a Strong turbulfince is the temperature reached 210 F the water content of the set up in the fluid mixture. When the grease mixture is recycle material was 217% spongy appearance Passed through Such a valve with a Sumcienfly high Pres the mixture had assumed subsided. When the temperasure drop the Soap fibers are very effectively Separated ture of the batch r ached 260 F recycling was stopped and dispersed without any material breaking or thickening The water content Of the recycl'e materi al at this such as occurs when the grease is subjected to substanperature was 0 42% Heating was continued and when fial kneading action during cooling The S of 25 the temperature of the batch reached 306 F. recycle was pers'al Of the fibers and consequently the yleld and prodresumed but with no presure drop across the globe valve uct quality of the grease is directly related to the pres in order to dehydrate the material remaining in the re- F across the Valve For purposes Of i prissent cycle lines. When the temperature of the batch reached lnventlon, the pressure drop across the shearing orifices F thfi heating Steam was turned Off and finishing can range from about 20 w 100 prefertbly about was added lowly On reduction of the temperature to 50 to 80 p.s.i.g. Pressure drops of over 100 p.s.l.'g. do not F 65po1mas of finishino oil had been added to appear lnecessaxy. although pressure drops to about the mixture. The kettle was alfowed to sit until the tem- 200 or g can be empllfiyedwlth 2 harmperature was reduced to 245 F. The product was then ful t e a1 e colloid milled at .005 clearance and the product was at composltlon may be further finished after dehydration by 3; 170 F collodidal milling so as to obtian the desired grease consistency. Colloidal milling operations are subject to vari- EXAMPLE II ance, depending upon the inlet temperature, mill size and the like. The colloid mill size or clearance is ordi- Several batches of lithium Y Y Sieflmte greases narily from about .001 to .1 inch. Although in high temwere P p using substantially the Same Procedure and perature processes, recycling through the gear pump and open lines has been found sufiicient, in the low temperature process of the present invention normally greater shear than that given by a conventional recycle gear pump alone is required for satisfactory yields.

The following example will serve to illustrate the formulation as that of Example I and recycled around the grease kettle through diiferent sized globe valves at vari- Table I Recycle Line 1" Valve 1% Valve Pressure Drop, p.s.i.g none 80 40 50 Max. Temperature, F 315 330 315 320 322 I 260 Recycle Rate:

lbs/min 30 30 4 10 31 22 Charge turnover, min 4.5 9 34 9 4 6 N0 Recycle Recycle Charge, lbs;

Beef Tallow 1. 5 1. 5 3 1. 5 l. 5 1. 5 1. 6 Hydrogenated Castor Oil 13. 5 13.5 27 13.5 13. 5 l3. 5 13. 5 Lithium Hydroxide Monohydrate. 2. 41 2. 42 4. 82 2. 42 2. 41 2. 41 2. 40 Oil Blend 120 120 240 120 120 120 120 Finishing Oil Blend Addition, lbs 30 31 155 52 05 79 Sample No. 801:

Lithium Soap, wt. percent 9. 00 7. 50 7.00 7. 50 Oil Blend, Wt. percent- 90. 92. 41 92. 88 92. 41 Moisture, wt. percent--. 0.07 0.01 0.05 0.08 Free Li 011, wt. percent 0. 08 0.08 0.07 0.01 AS'IM Penetrations:

Unworked 288 297 295 294 Worked 269 284 290 278 l0l),O00Regl1lar 300 313 314 308 100,000Navy 323 314 325 319 323 331 322 4 hour Sh 1 Roll, 160 r.p.1n. RT: ASTM Penetration Change +4 2 +11 +16 +22 +10 -2 96 hour Shell Muller, 10 r.p.m. F;

AST'M Penetration Change. +35 +40 +40 +37 +42 +19 +24 MIL-G-10024A Pressure Bleed: ercent separated oil 4. 3 3. 6 5. 4 5. 1 5. 7 5. 3 5. 1

Wheel Bearing 660 r.p.n1. 250 F.: Leakage, Pass Pass Pass Pass Pass Pass Pass grams "i 0. 9 1. 6 1.6 2.0 1.0 1.8 1.9 ASTM Dropping Point, F 384 382 383 381 382 382 384 1 Recycle stopped at this point before complete dehydration at about 325 F.

ous pressure drops, maximum temperatures and recycle rates. For comparison, a run employing no recycling and no pressure drop across the valve is included. Except as indicated recycling was for essentially the entire dehydration period above about 200 F. The conditions and tests on the products are shown in Table I.

From the data of Table I it is evident that little improvement in yield, i.e., hardness for a given soap content, is obtained by recycle with no pressure drop when compared with no recycle at all. The data further show that the yield obtained from the process of the present invention, for instance as measured by the amount of finishing oil permitted for a product of given penetration, is significantly greater than that obtained from low temperature processing (maximum 330 F.) without recycle.

EXAMPLE III Employing the process of the present invention several batches of lithium l-hydroxy stearate thickened greases of the same general formulation as Example I were prepared at 400 and 330 F. maximum dehydration temperatures by recycling the mixture during the entire dehydration period through a 1 inch globe valve. The constituents of the charge, recycle conditions and results are all shown in Table II.

Table 111 Recycled for 1 Hour Under 60 p.s.i.g. Pressure Drop Across 1. No Recycle Globe Valve After First Reaching 330 F.

Recycle Charge, lbs 120 Recycle Rate, lbs/min 120 Charge Turnover, min 1 5025 Sample No. 801:

Lithium Soap, Wt. percent.. 12. 50 Mineral Oil, wt. percent. 87. Moisture, wt. percent 0.07 Free LiOH, wt. percent 0.08 ASTM Penetrations:

Unworked- 277 298 Worked 283 285 100,000Regular 300 302 100,000-Navy 302 4 Hour Shell Roll, 160 r.p.m. RT: ASTM Penetration Change +18 22 96 Hour Shell Muller, 10 r.p.m. 150 F.: ASTM Penetration Change +12 MIL-G-10924A Pressure Bleed:

Percent Separated Oil 5. 9 10.0 Wheel Bearing 660 r.p.m. 250 Pass Pass F; Leakage, grams 0.2 1.9 ASIM Dropping Point, F.- 396 396 Table 11 High Temp. (400 F.) Low Temp.

Recycle Pressure Drop, p.s.i.g none none none Recycle Rate:

lbs./n1i.n 33 4 30 30 Charge turnover, min 1. 25 4. 5 38 9 4. 5

No Recycle Recycle Charge, lbs.:

Beet Tallow 1. 5 1. 5 1. 5 1. 5 3 1. 5 Hydrogenated Castor Oil 13. 5 13. 5 13. 5 13. 5 27 13.5 Lithium Hydroxide Monohydrate. 2. 43 2. 40 2. 40 2. 40 4. 82 2. 42 Oil Blend 135 135 135 240 120 Finishing Oil Blend Addition, lbs 65 65 65 31 5096 5228 5243 5155 Sample No. 801:

Lithium Soap, wt. percent 7.00 7. 00 7.00 9.00 Oil Blend, wt. percent 92.88 92. 96 92. 96 90.89 Moisture, Wt. pcrcent 0.08 0. 02 0.01 0. 04 0. 0-4 0.02 0.03 0.07

295 294 294 340 292 281 282 285 286 338 276 268 315 315 309 347 312 304 ,0 y 336 332 330 325 314 4 hour Shell Roll, r.p.m. RT: ASTM Penetration Change +4 +11 +2 +11 2 96 hour Shell Muller, 10 r.p.m. 150 F;

ASTM Penetration Change +22 +28 +40 +40 MIL-G-10924A Pressure Bleed: Percent separated oil 6.1 5. 9 5.1 5. 4 3. 6 Wheel Bearing 660 r.p.m. 250 F.: Leakage, Pass Pass Pass Pass Pass grams 2. 2 1. 6 2. 8 1. 6 1.6 ASTM Dropping Point, F 385 382 382 383 382 The data of Table II demonstrate that low temperature recycle processing in accordance with the process of the present invention gave equally as good yield and product quality as high temperature recycle processing.

EXAMPLE IV Examination of Table III shows that the yield and quality of lithium 12-hydroxy-stearate greases made by recycling to the shearing means after reaching a temperature of 330 F., i.e., after the dehydration period, are essentially no better than those of the same type of grease made at the same maximum temperature without recycling.

We claim:

1. In a method for preparing a lubricating grease which includes heating in grease-forming proportions a mixture of an ester of 12-hydroxy stearic acid, a mineral oil of lubricating viscosity, and an aqueous solution of a lithium neutralizing compound to a temperature of about 300 to 350 F. until the mixture is essentially dehydrated, and cooling the mixture to provide a grease composition, the improvement which comprises recycling said mixture through a restricted shearing orifice during the initial dehydration period and over the major portion of the dehydration period in the range of about 200 to 260 F., said recycling being effected with a pressure drop across said orifice of at least about 20 p.s.i.g. at a grease-forming mixture turnover rate of at least about .02 per minute and sufficient to increase the grease yield.

2. The method of claim 1 wherein the recycle is during initial dehydration and over the major portion of the dehydration period in the range of about 200 to 350 F.

3. The method of claim 1 wherein the batch turnover rate is at least about .1 per minute.

4. The method of claim 1 wherein the pressure drop across the shearing orifice is about 50 to 100 p.s.i.g. and the turnover rate is at least about 0.1 per minute.

5. The method of claim 4 wherein the ester is hydrogenated castor oil.

6. The method of claim 5 wherein the recycle is during initial dehydration and over the major portion of the dehydration period in the range of about 200 to 350 F.

References Cited in the file of this patent UNITED STATES PATENTS 2,542,159 Stevens Feb. 20, 1951 2,704,363 Armstrong Mar. 15, 1955 2,801,220 Smith July 30, 1957 2,886,525 Dilworth et al. May 12, 1959 3,015,624 Hencke et a1 Jan. 2, 1962 UNITED; STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 3,117,087

January 7,, 1964 Martin M, McCormick et a1, It is hereby .cexgtifiedthet-rror appears -in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below,

Column 5..., line 2G,, for "l' hydroxy" read 12 hydroxycolumn 6 Table III seCond column line 13 thereof for "+18" read --l8 Signed and sealed this 17th day of November 1964,

(SEAL) Attest:

ERNEST w. swwsa" Attesting Officer EDWARD J. BRENNER Commissioner of Patents 

1. IN A METHOD FOR PREPARING A LUBRICATING GREASE WHICH INCLUDES HEATING IN GREASE-FORMING PROPORTIONS A MIXTURE OF AN ESTER OF 12-HYDROXY STEARIC ACID, A MINERAL OIL OF LUBRICATING VISCOSITY, AND AN AQUEOUS SOLUTION OF A LITHIUM NEUTRALIZING COMPOUND TO A TEMPERATURE OF ABOUT 300 TO 350*F. UNTIL THE MIXTURE IS ESSENTIALLY DEHYDRATED, AND COOLING THE MIXTURE TO PROVIDE A GREASE COMPOSITION, THE IMPROVEMENT WHICH COMPRISES RECYCLING SAID MIXTURE THROUGH A RESTRICTED SHEARING ORIFICE DURING THE INITIAL DEHYDRATION PERIOD AND OVER THE MAJOR PORTION OF THE DEHYDRATION PERIOD IN THE RANGE OF ABOUT 200 TO 260*F., SAID RECYCLING BEING EFFECTED WITH A PRESSURE DROP ACROSS SAID ORIFICE OF AT LEAST ABOUT 20 P.S.I.G. AT A GREASE-FORMING MIXTURE TURNOVER RATE OF AT LEAST ABOUT .02 PER MINUTE AND SUFFICIENT TO INCREASE THE GREASE YIELD. 